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Scientia Silvae Sinicae ›› 2017, Vol. 53 ›› Issue (6): 10-20.doi: 10.11707/j.1001-7488.20170602

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Variation in the Sap Flow Velocity of Larix principis-rupprechtii and Its Impact Factors in Different Slope Positions in a Semi-Arid Region of Liupan Mountains

Wang Yanbing1, Wang Yanhui1, Xiong Wei1, Yao Yiqiang1,2, Zhang Tong1,3, Li Zhenhua1,4   

  1. 1. Key Laboratory of Forestry Ecology and Environment of State Forestry Administration Institute of Forest Ecology, Environment and Protection, Chinese Academy of Forestry Beijing 100091;
    2. College of Forestry, Shenyang Agricultural University Shenyang 110866;
    3. College of Soil and Water Conservation, Beijing Forestry University Beijing 100083;
    4. School of Life Science and Technology, Xinxiang University Xinxiang 453000
  • Received:2016-03-15 Revised:2016-05-23 Online:2017-06-25 Published:2017-07-14

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Abstract: [Objective] It is key to clearly recognize variation in sap flow velocity in trees in various slope positions and its main environmental factors, so that to improve the calculation accuracy for forest transpiration by means of up-scaling from a plot/position to a whole slope or a watershed, especially in semi-arid areas featuring with a strong variation of soil moisture in slopes. [Method] Three plots of Larix principis-rupprechtii were set up respectively at the upper, middle and lower positions on the northwest-facing slope in Diediegou watershed of Liupan Mountains, and the sap flow velocity in trees, as well as the soil water potential and meteorological factors were monitored simultaneously throughout the growing season (Jun. to Sep.) in 2015. [Result] The result showed that there were significant differences in the soil water potential of 60 cm layer (Ψ0-60, MPa) among slope positions, in an order of lower position (-0.210)>middle position (-0.410)>upper position (-0.511), and in the daily average sap flow velocity (mL·cm-2 min-1) in an order of lower position (0.045)>upper position (0.036)>middle position (0.034). Throughout the study period, the daily average sap flow velocity was significantly and positively correlated with the average daily air temperature (Ta), daily maximum temperature (Tmax), daily minimum temperature (Tmin), potential evapotranspiration (PET), average daily saturated vapor pressure deficit (VPD), average daily solar radiation density (Rs) and Ψ0-60, but significantly and negatively with the daily average air relative humidity (RH) and precipitation (P). Moreover, the correlation coefficients with each other were significantly different among slope positions. The order was lower>upper>middle for the meteorological factors, whereas upper>middle>lower for the Ψ0-60. According to the boundary line analysis, significant differences were also found in the degree of sap flow velocity variation in response to each single factor among slope positions. From the upper position to the lower, the degree decreased gradually for Ta, Tmax, RH, VPD, and Ψ0-60, whereas increased for the Rs with stepwise regression analysis, a multivariate linear model was established for each slope position between daily average sap flow velocity and environmental factors. It was clear that the selected factors for each model obviously differed at different slope positions. For example, the first and the second important factors were Rs and Ψ0-60 successively in the model of the lower position. However, they turned to Ψ0-60 and VPD at the upper position, and VPD and Ψ0-60 at the middle position, respectively. [Conclusion] As a conclusion, the variation of sap flow velocity among slope positions is a consequence of joint contributions of soil moisture and meteorological factors affected by terrain. Therefore, it is necessary to consider the effect of position differences in soil moisture and meteorological factors when scaling up the value of sap flow velocity from a plot/position scale to a slope scale.

Key words: Larix principis-rupprechtii, sap flow, slope position, semi-arid areas

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